Boat drive arrangement

ABSTRACT

AN INBOARD-OUTBOAD DRIVE FOR A BOAT WHEREIN THE OUTBOARD LEG IS OF A GENERALLY Z CONFIGURATION, IS MOUNTED ON A HORIZONTAL TILT AXIS REARWARDLY ADHACENT TO THE TRANSOM AND INCLUDES A DOWNWARDLY AND FORWARDLY INCLINED DRIVE SHAFT COUPLED AT ITS LOWER END TO A GENREALLY HORIZONTAL PROPELLER SHAFT. THE CONNECTION BETWEEN THE DRIVE SHAFT AND THE PROPELLER SHAFT IS THROUGH GEARING HAVING A RATIO EQUAL TO SUBSTANTIALLY THE COSINE OF THE ANGLE BETWEEN THE DRIVE SHAFT AND PROPELLER SHAFT. THE LOWER PORTION OF THE OUTBOARD HOUSING IS ARRANGED TO ROTATE FOR STEERING ABOUT THE AXIS OF THE DRIVE SHAFT. HYDRAULIC STEERING MEANS, ARE PROVIDED FOR ROTATING THE LOWER HOUSING, INCLUDING A DOUBLE ACTING HYDRAULIC CYLINDER AND PISTON MEANS, THE PISTON MEANS BEING PROVIDED WITH PORTS AND CHECK VALVES WHICH OPEN AUTOMATICALLY AT EACH EXTREME OF THE STEERING MOVEMENT TO PERMIT A FLOW OF HYDRAULIC FLUID THROUGH THE PISTON MEANS TO SCAVENGE AIR FROM THE SYSTEM.

Sept. 20, 1971 K. A. BERGSTEDT 3,505,577

BOAT DRIVE ARRANGEMENT Filed Jan. 6, 1970 3 Sheets-Sheet 1 INVL' N TORKarl fltabn Berystedz mam ATTORNEY Se t. 20, 1971 K. A. BERGSTEDT3,505,577

BOAT DRIVE ARRANGEMENT Filed Jan. 6, 1970 3 Sheets-Sheet 2 ll/ll T I."1255' iiunuuut nun INVENWR 16 lfarl 4bdon Berystedt Sept. 20, 1971 K.A. BERGSTEDT 3,605,677

BOAT DRIVE ARRANGEMENT Filed Jan. 6, 1970 3 Sheets-Sheet S FIQS IN Vf N70R Karl A'fidm Beryszedt ATTORNEY United States Patent US. Cl. 11535 11Claims ABSTRACT OF THE DISCLOSURE An inboard-outboard drive for a boatwherein the outboard leg is of a generally Z configuration, is mountedon a horizontal tilt axis rearwardly adjacent to the transom andincludes a downwardly and forwardly inclined drive shaft coupled at itslower end to a generally horizontal propeller shaft. The connectionbetween the drive shaft and the propeller shaft is through gearinghaving a ratio equal to substantially the cosine of the angle betweenthe drive shaft and propeller shaft. The lower portion of the outboardhousing is arranged to rotate for steering about the axis of the driveshaft. Hydraulic steering means are provided for rotating the lowerhousing, including a double acting hydraulic cylinder and piston means,the piston means being provided with ports and check valves which openautomatically at each extreme of the steering movement to permit a flowof hydraulic fluid through the piston means to scavenge air from thesystem.

This invention relates to inboard-outboard drive units for boats of thetype wherein the lower propeller-carrying portion of the outboardhousing is steerable about the axis of an upwardly extending drive shaftin the housing and wherein the steering torque is minimized by providinga gear ratio between the drive shaft and the propeller shaftsubstantially equal to the cosine of the angle between said shafts. Adrive unit in which steering torque is so minimized is shown and claimedin my US. Pat. No. 3,382,838 issued May 14, 1968, entitled Device on thePropeller Installation for Boats. The present invention further relatesto hydraulic steering means for such drive units.

It is a general object of this invention to provide an improved driveunit of the aforesaid type. It is a more specific object of thisinvention to provide a compact drive of such type, wherein the propelleris located adjacent to the boat transom. It is a further object of theinvention to provide an improved hydraulic steering system for rotatingan outboard housing portion which carries the propeller and which ismounted for rotation on a steering axis. Other and further objects willbe apparent from the following description when taken in connection withthe drawings, in which:

FIG. 1 is a side elevational view of an inboard-outboard drive unit fora boat embodying my invention, portions of the boat being represented inphantom;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a sectional side view of the unit on an enlarged scale takengenerall along line 3--3 of FIG. 2;

FIG. 4 is a sectional detail view on a further enlarged scale of aportion of the hydraulic steering system taken generally along line 4-4of FIG. 3; and

FIG. 5 is a sectional view of parts of the portion shown in FIG. 4 takenalong line 5-5 and on the scale of FIG. 4.

3,605,677 Patented Sept. 20, 1971 In the drawings, an inboard-outboarddrive unit is shown in FIGS. 1 and 2 comprising an inboard engine,generally represented at 1, which is mounted in a boat 2 having a sterntransom 3 with an opening 4 therethrough. The opening is closed by ashell 5 including a flange 6 engaging and sealed against the outer face7 of the transom and bolted, such as by means of bolts 8, to thetransom. The shell 5 includes arm portions 9 which project rearwardly ofthe transom and which journal pivot pin projections 10 from a hood-likeportion 11 of outboard housing or leg 12. Housing 12 comprises an upperportion 13 and a lower steerable portion 14 which carries propeller 15and which is provided with a skeg 16 and anticavitation plate 17, thepropeller being shown in FIG. 2 by a representation of its turningcircle.

A hydraulic trimming and tilting cylinder arrangement is provided at 18to adjust the trim angle of the outboard housing, which is shown inposition for normal straight ahead drive in the drawing. The hydraulictrim arrangement is operated from a suitable remote station through aflexible push-pull cable means 19 connected to valve lever 20, thearrangement being provided through the valve controlled by lever 20 withhydraulic fluid under pressure from a suitable source represented by andincluding conduit 21. Conduits 22 and 23 extend from a suitable pumpconnected with a steering wheel to provide hydraulic fluid underpressure to the hydraulic steering mechanism embodied within the upperportion 13 of the outboard housing 12 as hereinafter more particularlydescribed. It will be understood that the conduits 22 and 23 areflexible between the transom and the outboard leg, whereby tilting ofthe leg on the horizontal axis of pivot pins 10 is permitted. Theconduits 22 and 23 extend inwardly through the transom, and theypreferably extend and are sealed through the flange 6 of the mountinghell 5 and pass into the boat through opening 4. Bumper means 24 isarranged to limit the forward tilting movement of the outboard housingor leg so as to prevent the leg from tilting forward under anycircumstances into a position in which the lower housing 13 wouldcontact the lower edge of the transom. Maximum extension of thehydraulic cylinder and piston arrangement 18 tilts the leg about axis Tpreferably sufliciently to raise the propeller 15 above Water.

The drive unit is shown in section in FIG. 3, several parts as thereshown being identified by the reference numerals as described above inconnection with FIGS. 1 and 2.

The inboard engine 1 is provided with a forward and reverse transmission(not shown) which is operated by a lever 25 controlled by a suitablelinkage mechanism 26 from the usual operators station in the boat, fromwhich station the steering and tilt and trim arrangements are alsooperable. The engine drive shaft 27 is journalled in a hollow ringmember 28 which is externally connected and sealed by means of suitablecompressed rubber or the like rings 29 to shell 5. The shaft 27terminates rearwardly in a universal joint 30 which is in turn connectedto universal joint 31 and therethrough to a countershaft 32. It will beunderstood that suitable spline connections (not shown) are providedbetween at least one of the shafts and one of the joints to accommodatethe necessary movement imposed by the geometry when the outboard leg istilted. Joints 3t) and 31 together comprise an assembly commonlyreferred to as a double universal joint. The tilt axis for the outboardleg is identified by the letter T in FIG. 3, and it will be understoodthat this corresponds to the horizontal axis of the pivot pins shown inFIGS. 1 and 2. The tilt axis, which extends laterally of the boat centerline, will be seen to substantially intersect the axis, if extended, ofengine shaft 27 and to be substantially midway between the universaljoints 30 and 31. The position of the tilt axis with respect to thejoints is selected to establish an appropriate working axis of thejoints. It will further be seen that the countershaft 32 is at a smalldownward angle of substantially degrees with respect to shaft 27. It hasbeen found that operation of double universal joints at a slight angle,such as an angle of 15 degrees, does not adversely affect theperformance of the joints, while the downward inclination of the countershaft 32 permits improved geometry of the upper end 33 of the upperhousing portion 13 and increases the maximum permissible tilt angle forthe leg, in that there is greater clearance between the upper end 33 andthe flange 6 or the transom 3, and, since there is a maximum permittedangle for operation of universal joints, in that the greater angle oftilt does not exceed such maximum angle for the joints. Specifically,for example, the double universal joint 30, 31 may be designed forsatisfactory operation up to a maximum angle of approximately 60degrees, and, since the countershaft is inclined downwardly byapproximately 15 degrees with the outboard leg in normal trim position,the joints would then accommodate rearward and upward tilting of the legup to about 75 degrees from its normal trim position. It is to be notedthat the top of the upper housing inclines downwardly along andadjacently above the countershaft to provide optimal transom clearanceupon tilting up, as well as a pleasing external configuration of theoutboard leg.

The hood or bell-like portion 11 of the outboard housing, which has beenpreviously described as carrying pivot pins 10, is arranged to swinginto the bell 5 with tilting of the outboard housing. The ring member 28includes a unitary, rearwardly extending, hollow, generally cylindricalinner portion 34, and the member 11 has a similar inner hollowcylindrical portion 35 extending forwardly toward portion 34. A flexiblecorrugated cylindrical boot 36 is clamped to and extends betweenportions 34 and 35 to enclose the universal joints 30, 31 in awatertight compartment.

It will be seen that outboard housing portion 11 and bell 5 serve toprotect the boot 36 against damage from external objects, and it will befurther seen that bell 5 together with member 28 completely close theopening 4 in transom 3 against the entrance of water into the boat,although water may reach the outside of boot 36.

Countershaft 32 is supported on roller thrust bearings 37 and 38 withinupper portion 13 of the outboard housing, and it has keyed thereon abevel gear 39 meshing with bevel gear 49 keyed on the upper end 41 of ajointed drive shaft 42. The drive shaft extends from its upper end in adownward and forwardly inclined direction. The drive shaft is supportedfor rotation or journalled by thrust bearings 43 and 44 in the upperhousing portion 13 and by thrust bearing 45 in the lower housing portion14. Joint means 46 permit the shaft to be separated between its ends forconvenience in assembling and disassembling the outboard leg and toprovide for length adjustment of the shaft to accommodate it to thebearing positions.

The lower housing portion 14 has an upwardly extending hollow neckmember 47 bolted thereto by bolts 48 at its upper end 49. The hollowneck 47 extends upwardly into a downwardly opening generally tubularprojecting portion 50 of the upper housing 13 and is rotatable thereinon pin bearing 51 and on ball bearing 52 on an axis coincident with theaxis of shaft 42. A sealing ring 53 interposed between projection 50 andthe upper end 49 of the lower housing prevents the escape of hydraulicfluid from and the entry of water up into the projection and thusprotects bearings 43, 44, 51 and 52.

The outer surface of the hollow neck member 47 is provided betweenbearings 51 and 52 throughout a part of its periphery with pinion teeth54 engaged with the teeth of a rack member 55, as hereinafter moreparticularly described, permitting steering of the lower portion 14 ofthe housing with respect to the upper portion 13. Movement of the rack55 in a direction toward the viewer in FIG. 3 will cause the lowerhousing portion 14 to swing in a direction in which the propeller wouldmove away from the viewer, that is to say, propeller 15 being a pusherpropeller, in a direction to steer the boat to starboard.

The neck member 47 carries at its lower end, and at a location withinlower housing portion 14, a roller thrust bearing 56 which journals thedrive shaft just below coupling 46. The drive shaft 42 terminatesdownwardly in a bevel gear 57. Propeller shaft 58 is mounted in thelower housing portion by roller thrust bearings 59 and 60 and rollerbearings 61, and it is provided with a crown gear 62- meshing with thebevel gear 57. Propeller 15 is preferably a pusher propeller and is,accordingly, mounted on the propeller shaft exteriorly and rearwardly ofthe housing portion 14.

The drive shaft 42 and propeller shaft 58 rotate in the same directionof rotation, that is, the teeth of gear 57 are in mesh with the teeth ofgear 62 above shaft 42 and above shaft 58, and the gear ratio betweenthese shafts is substantially equal to the cosine of the angle betweenthe shaft axes to minimize the steering torque effect of shaft 42 on thelower housing in accord with the teachings of my US. Pat. No. 3,382,838.

The angle between the axis of drive shaft 42 and the axis of propellershaft 58 in the arrangement shown in FIG. 3 is 58 degrees, or 122degrees, and the cosine of this angle is substantially 0.53, whereby thegear ratio between drive shaft 42 and propeller shaft 58, or from gear57 to gear 62, is 120.53. As so arranged, gear 62, being a crown gear,and gear 57, a bevel gear, the teeth are in engagement perpendicularlyabove the point of intersection of the drive shaft and propeller shaftaxes. It will be found normally desirable that the gear ratio should notbe substantially greater than 1:053 for modern gasoline engines andmodern high speed propellers, in that a substantially greater reductionfrom shaft 42 to the propeller would require excessive shaft speeds or alow speed propeller. If the angle between the shafts 42 and 58 weredegrees, for example, the gear ratio would be substantially 120.34,while at degrees the ratio would be 1:0.26 or nearly 4:1, a ratio whichwould be under any usual circumstances unsatisfactory for a high speedplanning boat or for a high speed propeller. Decreasing the angle to 50degrees would permit a ratio of 110.64, while an angle of 40 degreeswould permit a ratio of 1:0.77. While such gear ratios may be moredesirable for a high speed propeller than a ratio of 120.53, thegeometry of the outboard leg would be adversely affected by the smallerangle and, since the lower unit 14 steers about the axis of shaft 42,the propeller shaft would tilt up at an undesirable angle when the lowerunit was swung away from normal straight ahead drive position.Accordingly, the minium satisfactory angle between the shaft axes wouldbe approximateiy 45 degrees and the maximum satisfactory angle would beapproximately 70 degrees, although with a low speed propeller angles ofas great as about 75 degrees might be employed.

A downward and forward inclination of 58 degrees to the horizontal forshaft 42 provides an arrangement in which propeller 1S andanticavitation plate 17 may be desirably disposed close to the loweredge 3' or the transom, with the plate aligned at the level of orslightly below edge 3' and with the propeller sufficiently close to thetransom as to be in compacted water rather than in the turbulent wakefurther astern, and with the plate and propeller in positions in whichthey tend to remain at desired depth upon pitching of the boat.

The hydraulic steering system is best understood with reference to FIGS.4 and 5. As seen therein, the up standing neck member 47, which isrigidly attached to lower housing 14, is provided exteriorly throughoutsomewhat less than half of its periphery with teeth 54 meshing withteeth 63 of rack member 55. The rack member carries a piston at eachend, piston 64 being disposed in a cylinder 65 and piston 66 beingdisposed in a cylinder 67. The cylinders have closed outer ends 68 and69, respectively, and are provided with suitable connections torespective hydraulic fluid lines 22 and 23, whereby the piston andcylinders constitute a double acting hydraulic cylinder and pistonmechanism for moving the rack member back and forth.

The hydraulic system includes a pump 70 connected to steering wheel 71operable to force fluid into conduit 22 and to permit return of fluidfrom conduit 23 in response to rotation of the wheel in one directionand vice versa in response to rotation in the opposite direction.

A hydraulic fluid supply or sump 72 is connected to the pump 70- tosupply fluid for the original filling of the system as the air isscavenged therefrom, and to supply make up fluid thereafter.

The rack member has motion in each direction limited when one or theother of pistons 64 and 66 meets the respective cylinder end wall 68 and69. The teeth 63 on rack 55 extend through a distance therealong, andthe teeth 54 on neck member 47 extend around the periphery thereof,suflicicntly to accommodate the full extent of the permitted movement ofrack 55. For example, the rack may be arranged to move sufl'lciently torotate neck member 47 and lower housing 14 through a total ofapproximately 60 degrees, 30 degrees on each side of the dead centerposition corresponding to straight ahead steering position.

In the construction shown, rack member 55 is provided with a partiallythreaded reduced generally cylindrical end portion 73 which passesthrough piston 64 and onto which nut 74 is screwed up against the pistonto hold the piston firmly against shoulder 75 of the rack member. Theend portion is longitudinally bored at 76 into a cross-bored chamber 77in the rack member. The projection 50 constitutes a fluid containingchamber and housing for the rack and pinion mechanism and the interior78 of the housing chamber has communication through a check valve 79into the chamber 77 within the rack member. The check valve 79 mayinclude a light spring 90 seated on pin 91.

The cylinder 65 terminates at an edge 80 which, at cutaway portion 80,exposes a small part of the wall 81 of piston 64 when this piston isfully extended, that is, with piston 66 stopped by or very close to endwall 69. A port or passage 82 is drilled into this portion of the pistonwall and communicates with the interior of cylinder 65 through groove 83formed around portion 55 of the rack and through passage 84 drilled frompiston face 89 to the grove.

The arangement associated with piston 66 will be seen to be identical tothat associated with piston 64 as above described, including bore 85,port 86, check valve 87 and passage 88 corresponding, respectively, tobore 76, port 82, check valve 79, and passage 4.

The above described arrangement provides for selfbleeding and airscavenging of the system. Operation of pump 70 to force fluid throughline 22 into cylinder 65 causes the piston 64 to move in a directionoutwardly of the cylinder until piston 66 nearly meets wall 69,whereupon port 82 is exposed, through cut-away portion or notch 80', tothe chamber interior 78. Whatever air may be in line 22 and cylinder 65now passes together with hydraulic fluid into bore 76, through passages83 and 84 and through port 82 into the interior 78 of the housingchamber. The increasing pressure in the housing chamber opens thelightly loaded check valve 87 and first any entrapped air, and laterhydraulic fluid, pass through the check valve and bore 85 into cylinder67 and thence through line 23 and into sump 72. Operation of pump 70 inreverse direction forces piston 66 in a direction outwardly of cylinder67 until port 86 is uncovered, whereupon hydraulic fluid and anyremaining trapped air pass through channels 88 and 86 into chamber 78and thence through check valve 79 and bore 76 into cylinder 65 andfinally through conduit 22 to the sump 72. The pump is thus operatedback and forth to and beyond its full steering eflect in one and in theother direction a sufflcient number of times to insure complete bleedingor scavenging of the air from the system.

In operation, the steering wheel now controls the movement of rack 55between full starboard and full port steering positions of the lowerhousing up to the point at which port 82 or port 86 is uncovered,whereafter continued movement of the wheel will force a small flow ofhydraulic fluid through the chamber interior 7-8, as when the system isbeing bled. The lower housing may be turned slightly beyond the fullnormal port or starboard steering position by an external force untilone or the other of pistons 64 or 66 meets the respective cylinder endwall 68 or 69. Such end play in the system, with prop erly proportionedcomponents, will be small, such as less than one degree of swing of thelower housing. Thus port 82 should become uncovered only when piston 66has approached very close to wall 69 at the maximum steering to portposition of the pistons, rack and lower housing portion, while port 86should become uncovered at the maximum steering to starboard position.

What is claimed is:

1. An inboard-outboard drive unit for a boat comprising an outboard legcomprising an upper portion disposed rearwardly of the stern of the boatand a lower portion, means tiltably mounting said upper portion on theboat for tilting on a generally horizontal lateral axis, a drive shaftdisposed in said leg extending from within said upper portion inclinedlydownwardly and forwardly into said lower portion, means rotatablyconnecting said lower portion to said upper portion for rotation of saidlower portion about the axis of said drive shaft, steering means forrotating said lower portion with respect to said upper portion aboutsaid axis, means having support in said upper portion for driving saiddrive shaft, a propeller shaft mounted in said lower portion disposedgenerally horizontally and parallel to the axis of the boat when saidlower portion is oriented for normal forward propulsion, a waterreaction propeller carried by said shaft exteriorly of said lowerportion, driving means in said lower portion drivingly connecting saiddrive shaft to said propeller shaft, the angle between the axes of saidshafts being between substantially 45 degrees and 70 degrees, saidconnecting means driving said propeller shaft in the same direction ofrotation as the direction of rotation of said drive shaft and at a ratiofrom said drive shaft to said propeller shaft equal to substantially thecosine of said angle.

2. The combination according to claim 1 wherein said means for drivingsaid drive shaft comprises an inboard engine, a drive train including apower shaft extending rearwardly from said engine, a counter shaftrearward of said power shaft and flexible drive means interposed betweenand drivingly connecting said power shaft and counter shaft, said drivetrain extending through an opening in said stern of the boat, and a gearconnection from said counter shaft to said drive shaft, said upper legportion having bearings mounted therein rotatably supporting saidcounter shaft, said flexible drive means having a working center atsubstantially said tilt axis, whereby said drive train is operative totransmit power from said 7 engine to said countershaft when said leg isin normal trim position and in upwardly tilted position.

3. The combination according to claim 1 wherein said propeller shaftprojects rearwardly from said lower portion and said propeller is apusher propeller.

4. The combination according to claim 1 wherein the engine is providedwith a forward and reverse transmission operative to drive said drivetrain selectively in one and the other direction of rotation and therebyto drive said propeller selectively for forward propulsion and forbacking down.

5. The combination according to claim 2 wherein said counter shaftextends from said flexible drive means rearwardly with a downwardinclination with respect to said engine power shaft when said leg is innormal trim position and with an upward inclination with respect to saidpower shaft when said leg is in an upwardly tilted position.

6. An inboard-outboard drive for a boat having a transom with an openingtherethrough and an inboard engine with a generally horizontal driveshaft extending rearwardly alignedly toward said opening, said shaftterminating in a rearward end, said drive having a countershaft with aforward end disposed rearwardly of said rearward end, a double universaljoint connecting between said shaft ends, a gear keyed on saidcountershaft, a drive shaft, a propeller shaft, when said drive is innormal drive position, said drive shaft extending downwardly below saidcountershaft at an angle to the vertical of between substantially 20 and45 degrees and said propeller shaft being generally horizontallydisposed, gear means drivingly connecting said drive shaft to saidpropeller shaft for rotation in the same direction and having a gearratio substantially equal to the cosine of the angle therebetween, anupper housing journalling said counter shaft and said drive shafttherein, a lower housing rotatably supported by said upper housing on arotational axis coincident with the axis of said drive shaft, said driveshaft entering said lower housing, said drive shaft and said propellershaft being journalled in said lower housing, said propeller shaftextending outwardly of said lower housing, a propeller exteriorly ofsaid lower housing carried by said propeller shaft, pivot meansestablishing a horizontal tilt axis extending laterally of the boat andbetween said shaft ends tiltably mounting said upper housing to saidboat whereby said housings may tilt upwardly from said normal driveposition upon the lower housing striking a submerged or floating object,and steering means connected between said upper and lower housingoperable to rotate said lower housing on its said rotational axisselectively from and to its straight ahead drive position.

7. The combination according to claim 6 wherein said drive shaft, whensaid drive is in normal drive position, extends inclinedly downwardlyand forwardly below said countershaft.

S. The combination according to claim 7 wherein said countershaft, whensaid drive is in normal drive position, extends rearwardly from its saidforward end at a downward inclination of between substantially l and 30degrees to the horizontal.

9. In an inboard-outboard drive unit for a boat comprising a generallyupright outboard leg disposed rearwardly of the boat transom and havingan upper housing portion attached to the boat, a lower housing portionand a drive shaft in said leg extending into and between said portions,said lower housing portion journalling a propeller shaft drivinglyconnected to said drive shaft, means rotatively mounting said lowerhousing portion to said upper housing portion on a steering axiscoincident with the drive shaft axis, a double acting hydraulic pistonand cylinder assembly, said assembly including cylinder means havingopposed cylinder end chambers, means to apply pressure hydraulic liquidselectively into one and the other of said end chambers and to open thesaid end chamber opposite to the chamber being supplied with pressureliquid for the escape of fluid therefrom, piston means in said endchambers adapted to be forced back and forth inwardly of said one andoutwardly of said other end chamber upon application of pressure fluidinto said other end chamber and inwardly of said other and outwardly ofsaid one end chamber in response to said application of pressure fluidto said one end chamber, said assembly being connected between saidupper and said lower housing portions and operative, in response tomovement of said piston means with respect to said cylinder means, toswing said lower housing portion between respective maximum steeringpositions, and scavenging valve means communicating between said endchambers, said valve means being opened in response to maximum steeringtravel of said piston means in the direction outwardly of said onecylinder end chamber thereby to provide fluid flow through said chambersin series.

10. In an inboard-outboard drive unit for a boat comprising a generallyupright outboard leg disposed rearwardly of the boat transom and havingan upper housing portion attached to the boat, a lower housing portionand a drive shaft in said leg extending into and between said portions,said lower housing portion journalling a propeller shaft drivinglyconnected to said drive shaft, means rotatively mounting said lowerhousing portion to said upper housing portion on a steering axiscoincident with the drive shaft axis, a pair of spaced apart cylindershaving open inner ends facing each other and closed outer ends, a pistonin each cylinder, a rack connected between said pistons, a pinionengaged with said rack and having an axis coincident with said steeringaxis, said pinion being connected to one of said housing portions andsaid cylinders being connected to the other housing portion whereby backand forth movement of said pistons and rack with respect to saidcylinders steeringly rotates said lower housing portion on said steeringaxis between opposite limit positions, a chamber located between saidcylinders and pistons adapted to be filled with hydraulic fluid, apassage in one piston opening through the face thereof into therespective cylinder and opening through a portion of the side wallthereof which is covered by the cylinder wall when the piston isinwardly of the cylinder and exposed to said chamber when the piston hasmoved outwardly of the cylinder into a position corresponding to limitsteering in one direction, a passage through said other piston openinginto said chamber and through the face of the piston into the interiorof its respective cylinder, a check valve for said last passage blockingflow of fluid therethrough in the direction from said cylinder interiorinto said chamber and freely passing flow in the opposite direction, andmeans to force pressure fluid into the cylinder for said one piston andto permit fluid flow from the other cylinder, said last means beingoperable to force said one piston into limit position thereby to uncoversaid passage opening in the wall of said one piston and thereafter tocause said fluid to flow through said chamber and into and through saidother cylinder, thereby to scavenge air from said cylinders and chamber.

11. In an inboard-outboard drive unit for a boat comprising a generallyupright outboard leg disposed rearwardly of the boat transom and havingan upper housing portion attached to the boat, a lower housing portionand a drive shaft in said leg extending into and between said portions,said lower housing portion journalling a propeller shaft drivinglyconnected to said drive shaft, means rotatively mounting said lowerhousing portion to said upper housing portion on a steering axiscoincident with the drive shaft axis, a steering system characterized inthat said last means comprises a generally cylindrical neck portion ofsaid lower housing portion extending upwardly therefrom into said upperhousing portion and coaxial with said drive shaft, bearing means in saidup- 9 per housing portion rotatively journalling said neck portiontherein, gear teeth externally on said neck portion, a rack member insaid upper housing portion engaged with said teeth, double actinghydraulic cylinder means fixed in said upper housing portion, pistonmeans in said cylinder means connected to said rack member, and manuallycontrolled hydraulic pressure fluid supply means connected to saidcylinder means for reciprocating said piston means and said theretoconnected rack member to References Cited UNITED STATES PATENTSArmantrout et al. 11535X Bergstedt 11535 Shirnanckas 11534 Ekman 1l535Alexander 115-34 provide steering rotation of said lower housing portion10 TRYGVE BLIX Primary Examiner on said axis.

